The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is moved by several turbojet engines each housed in a nacelle also accommodating an assembly of additional actuating devices related to its operation and ensuring various functions when the turbojet engine is in operation or stopped. These additional actuating devices comprise a mechanical thrust reverser system.
More precisely, a nacelle generally has a tubular structure comprising an air inlet upstream of the turbojet engine, a middle section intended to surround a fan of the turbojet engine, a downstream section accommodating the thrust reversal means and intended to surround the combustion chamber of the turbojet engine, and is generally terminated by an ejection nozzle the outlet of which is situated downstream of the turbojet engine.
Modern nacelles are intended to accommodate a double flow turbojet engine capable of generating through the blades of the rotating fan a hot air flow (also called primary flow) coming from the combustion chamber of the turbojet engine, and a cold air flow (secondary flow) which circulates outside the turbojet engine through an annular channel, also called flow path, formed between a fairing of the turbojet engine and an inner wall of the nacelle. The two air flows are ejected out of the turbojet engine from the rear of the nacelle.
The role of a thrust reverser during landing of an aircraft is to improve the braking ability of the aircraft by redirecting forward at least a part of the thrust generated by the turbojet engine. In this phase, the thrust reverser obstructs the annular channel of the cold air flow and directs the latter to the front of the nacelle, thereby generating a counter-thrust which adds to the braking of the wheels of the aircraft.
The means implemented to achieve this cold air flow redirection vary depending on the thrust reverser type. However, in all cases, the structure of a thrust reverser comprises movable cowls displaceable between, on the one hand, a deployed position in which they open a passage within the nacelle intended for the diverted flow, and on the other hand, a retracted position in which they close this passage. These cowls may fulfill a function of deflection or simply actuation of other diverting means.
In the case of a cascade-type thrust reverser, also known under the name of cascade thrust reverser, the air flow redirection is carried out by cascades vanes associated with reverser flaps, the cowl slides aiming to uncover or cover the cascade vanes. The reverser flaps form blocking doors activated by the sliding of the cowling generally generating a closing of the annular channel downstream of the cascades in order to optimize the redirection of the cold air flow.
Generally, the cascade vanes are attached to the casing of the turbojet engine and to the middle section of the nacelle using a front frame.
The common front frames include a multitude of parts.
More precisely, a common front frame includes a generally triangular cross-sectional torsion box comprising a lower wall connecting two upstream and downstream walls, the assembly forming the triangular section.
On the lower wall are brought a plane first upstream attachment edge intended to attach said box to a fan casing and an also plane second downstream attachment edge intended to attach said box to the cascade vanes.
The front frame comprises, in addition, a panel ensuring the fire resistance of the front frame and allowing to fasten the front frame to the outer cowl of the middle section.
This panel is brought on the upstream and/or downstream wall(s) of the torsion box.
The lower wall of the torsion box is subjected to tensile loads generated by the mounting of the cascade vanes on the torsion box.
Moreover, the actuators driving the thrust reverser cowl in these movements between its different positions being mounted on the front frame, the latter is subjected to a torque that should be transmitted efficiently from the actuators toward a suspension mast on which the nacelle is mounted.
It is known that the most adapted structures for transmitting a torque are the tubular structures while for tensile and compressive loads, a plane structure is preferable.
A good compromise of torsion box to fulfill these functions is a tubular torsion box, of triangular cross section, associated with an adapted plane portion, in the lower portion of the box.
The plane walls of the torsion box, the angular vertices between these walls and the plate promote the transmission of the tensile loads of the cascade vanes towards the turbojet engine casing, this by aligning to the different load paths of the tensile loads transmitted from the cascade vanes to the turbojet engine casing.